Bacterial diversity and activity in uranium mining wastes

Bacterial diversity was studied in several uranium mining waste piles and mill-tailings in Germany (Johanngeorgenstadt, Schlema/Alberoda, Gittersee/Coschütz) and in the USA (Shiprock, New Mexico and Gunnison, Colorado) using direct molecular approaches. Significant differences were found between bacterial communities distributed in the uranium mill-tailings and in the uranium mining waste piles. The predominant bacterial groups in the water and soil samples collected from the mill-tailings were gamma-, beta-, and delta-Proteobacteria, representatives of Cytophaga/Flavobacterium/Bacteroides (CFB) group and also Gram-positive bacteria with low G+C content. In contrary, in the uranium mining waste piles representatives of alpha-Proteobacteria and such of Holophaga/Acidobacterium division were predominant. In both environments, however, presence of related groups of gamma-Proteobacteria was demonstrated.
In parallel, the method of enrichment culturing was applied and particular indigenous bacterial strains were cultured from the uranium wastes and their interactions with U and some other metals were studied. In particular, microdiverse bacterial isolates belonging to Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans, Desulfovibrio vulgaris (oxamicus), Bacillus sphaericus, B. cereus, B. thuringiensis, B. megaterium, Clostridium sp., and Pseudomonas sp. were recovered and characterized.
Vegetative cells, spores and S-layers of one uranium mining waste pile isolate, namely Bacillus sphaericus JG-A12, able to accumulate reversibly high amounts of toxic metals from drain waters of the U wastes, were used for construction of bacteria-based biological ceramics (biocers) for bioremediation. Biosorption and desorption of U and Cu by the constructed biocers were studied in model experiments and it was demonstrated that they possess very high metal binding capacity and are suitable for reversible usage. The latter demonstrates that uranium mining waste piles are a reservoir of bacteria prospective for in situ bioremediation of these environments.